The use of polymeric film bases for carrying photographic layers is well known. In particular, photographic elements which require accurate physical characteristics use polyester film bases, such as polyethyleneterephthalate film bases or polyethylenenaphthalate film bases, and cellulose ester film bases, such as cellulose triacetate film bases.
It is known that the formation of static electric charges on the film base is a serious problem in the production of photographic elements. While coating the light-sensitive emulsion, electric charges which accumulate on the base discharge, producing light which is recorded as an image on the light-sensitive layer. Other drawbacks which result from the accumulation of electric charges on polymeric film bases are the adherence of dust and dirt, coating defects and limitation of coating speed.
Additionally, photographic elements comprising light-sensitive layers coated onto polymeric film bases, when used in rolls or reels which are mechanically wound and unwound or in sheets which are conveyed at high speed, tend to accumulate static charges and record the light generated by the static discharges.
The static-related damages occur not only before the photographic element has been manufactured, exposed and processed, but also after processing when the photographic element including the image is used to reproduce and enlarge the image. Accordingly, it is desired to provide permanent antistatic protection which retains its effectiveness even after processing.
To overcome the adverse effects resulting from accumulation of static electrical charges, it is known to provide photographic elements with antistatic layers including electrically conductive materials which are capable of transporting charges away from areas where they are not desired. Typically, such antistatic layers contain electrically conductive substances, in particular polyelectrolites such as the alkali metal salts of polycarboxylic acids or polysulfonic acids, or quaternary ammonium polymers, which dissipate the electrical charge by providing a layer which conducts electrons by an ionic mechanism. However, such layers are not very suitable as antistatic layers because they lose effectiveness under conditions of low relative humidity, become sticky under conditions of high relative humidity, and lose their antistatic effect after passage through processing baths. Additionally, conductive polymer layers used as subbing layers tend to worsen the adhesion of the light-sensitive layers to the support base or may negatively affect photographic properties of silver halide emulsion layers of photographic elements.
U.S. Pat. No. 4,424,273 describes a subbing antistatic layer comprising gelatin, a gelatin hardener, a vinyl addition latex polymer and a low viscosity and highly sulfonated polyacetal obtained upon reaction of a low viscosity polyacetal alcohol and a sulfonated aldehyde, the relative quantities of said gelatin and vinyl addition latex polymer to the acetal compound providing good adhesion characteristics without any significant loss of antistatic properties. Nevertheless a problem with this antistatic layer is that antistatic properties are diminished, even completely lost, when a coating is applied thereto. Accordingly, while this type of antistatic layer solves the problems of static electricity charges during coating of the photographic elements, it does not provide permanent antistatic protection to the photographic element after its manufacture.
Cross-linked polymer layers are well known in the photographic art to insure bonding of photographic layers to the support and/or prevent building up of electrostatic charges. U.S. Pat. No. 3,615,552 discloses a bonding layer for photographic elements comprising mixed acetals of polyvinyl alcohol with aldehydes with water-solubilizing groups and aldehyde without water-solubilizing groups, a hydrophobic polymer binder comprising hydroxyl groups, and a cross-linking agent such as a copolymer of unsaturated acid anhydrides. U.S. Pat. No. 3,071,466 discloses a bonding layer comprising a mixed acetals of polyvinyl alcohol with aldehydes with water-solubilizing groups and aldehyde without water-solubilizing groups, a hydrophobic polymer binder comprising hydroxyl groups in such a ratio that the polyacetal is soluble in organic solvents but only swellable in water, a binder polymer containing hydroxyl groups and being soluble in organic solvents, and a cross-linking agent containing at least two 1,2-epoxide groups. U.S. Pat. No. 4,225,665 discloses an antistatic layer comprising a conductive polymer having carboxyl groups, a hydrophobic polymer containing carboxyl groups and a cross-linking agent being a polyfunctional aziridine. U.S. Pat. No. 4,459,352 discloses a conductive polymer layer comprising a hydrophilic binder, a cellulose ester and a hardening agent. U.S. Pat. Nos. 5,096,975 and 5,126,405 disclose cross-linked conductive polymer layers comprising a copolymer of a vinylbenzene sulfonic acid and an ethylenically unsaturated monomer containing hydroxyl groups, a binder polymer containing hydroxyl groups and a cross-linking agent being respectively a methoxyalkyl-melamine or a hydroxylized metal lower alkoxide.
However, attempts to prevent or reduce electrostatic charge build up by a conductive layer may have a limited success. In addition to reducing such build-up to a sufficient degree, such layers are required to assure adequate adhesion to hydrophobic supports and subsequently coated photographic layers, to provide permanent antistatic protection when overcoated with photographic layers or after photographic processing, and not to affect negatively the photographic performance of the element.
Accordingly, there is still the need to provide single layer antistatic layers, using conductive polymer layers, which provide photographic elements a permanent antistatic protection.